Electric contact element

ABSTRACT

A contact element, in particular for making electrical contact to a sensing element of a gas sensor. The contact element has at least one connecting conductor, guided in a metal-sheathed line and contacted to at least one flexible connecting line. A connecting point between the at least one connecting conductor and the at least one connecting line is arranged in a contact housing that allows sealed and temperature-resistance contacting. The contact housing has at least one connecting element that is immovably joined to the at least one connecting line and may be contacted to the at least one connecting conductor. The at least one connecting element is arranged with an interference fit and in a form locking manner in the contact housing. The contact housing is enclosed by a temperature-resistant protective sleeve, which is joined directly to the metal-sheathed line ( 20,22 ) and to the at least one connecting line ( 20, 22 ).

FIELD OF THE INVENTION

The present invention relates to an electrical contact element.

BACKGROUND OF THE INVENTION

Sensing elements that are exposed to high temperatures and vibrationloads, such as those that can occur, for example, within the exhaustsystem of motor vehicles, are known. The electrical supply leads to suchsensing elements are exposed to considerable temperature stresses, thatconventional cable insulation cannot withstand. In particular, theconnecting points of the sensing elements to the electrical supplyleads, and their insulating layers, must be effectively shielded againstexcessive temperatures. In lambda probes, for example, heat-resistantmetal-sheathed lines, which must have a certain minimum length areusually used. Only beyond a specific distance from the heat-stressedmeasurement location can conventional cables take over the electricalconnection to a downstream analysis unit.

The connecting point between the heat-resistant metal-sheathed line andthe conventional cable line must, however, be configured so as to becompletely sealed against external influences. Also any excessive lengthof the metal-sheathed line is problematic, and creates the risk ofvibration breakage. The metal-sheathed line must therefore be as shortas possible because of the vibration loads that occur, so that therequirements for the connecting point comprise not only sealing againstenvironmental influences and moisture, but also the greatest possibletemperature resistance.

Connections between a rigid metal-sheathed line and flexible cable linesthat are injection-coated with plastic. Since, however, it is generallynot possible with an injection-coated plastic sheath of this kind tocreate sealed connections between the metal-sheathed line and theinsulated cable lines, additional measures, for example elastomer seals,are necessary. The volume of the connection and its mass and thus themoment of inertia increase as a result of these measures. This has adisadvantageous effect on the vibration resistance of the sheathedlines, thus subjecting them to a risk of breakage.

SUMMARY OF THE INVENTION

The object of the present invention is to create a sealed andtemperature-resistant connection between a metal-sheathed line andflexible cable lines that has the lowest possible mass.

By way of the largely prefabricated contact elements, it is possible tocreate, in a rapid and economical manner, lightweight,temperature-resistant, and vibration-resistant electrical connectionsfrom heat-stressed sensing elements to wiring harnesses. Conventionalconnecting techniques such as crimping and snap-locking are used in thiscontext. Because the electrical contacts are very well insulated fromone another, there is no risk of shunts or short-circuits. Because ofthe geometrical configuration of the contact housing with centering aidsand insertion aids, incorrect assembly is almost ruled out. Automaticassembly, for example using assembly robots, is thereby reliablyguaranteed. The subsequent laser welding of the electrical contacts andan enveloping thin protective metal sleeve also permits rapid automaticassembly. A robust, durable connection that is secured against breakageand vibration, and shielded from heat and any type of environmentalinfluence is also ensured. An elastomer seal ensures sealedencapsulation of the connecting element that is also resistant totemperatures exceeding 200° C. Lastly, the extremely compact andlightweight design, which minimizes the metal-sheathed line'ssusceptibility to vibration or vibration-induced breakage, isparticularly advantageous.

The contact housing of the contact element must be able to withstandrelatively high temperatures, and for that purpose can be made, forexample, from a thermosetting plastic or a ceramic material. Thesematerials also have the advantages of high stiffness, high mechanicalload-carrying capacity, and relatively unrestricted three-dimensionaldesign freedom. The mechanical properties can be further improved by wayof fiber reinforcements. The contour of the contact element can becylindrical, but because of the unrestricted shaping freedom using themolding or injection molding method, it can also be of any other desiredconfiguration, depending on the desired installation location oradditional anchoring or immobilization.

For a stable and vibration-free mechanical and electrical connectionbetween the electrical lines guided in the metal-sheathed line and theflexible cable lines leading to an analysis unit, the latter are joinedto one another inside the contact housing by laser welding. As comparedto conventional plug-in contacts, these connections exhibit much greaterlong-term durability and thus better service life. Laser welding of themetal-sheathed line to a metal sleeve enclosing the contact housingpractically rules out any penetration of moisture or other substancesthat might impair electrical insulation, even during a long operatingperiod.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a contact element in a sectioned view.

FIG. 2a shows a first plan view of a connecting element after insertioninto a contact housing.

FIG. 2b shows a plan view of a connecting element shown in FIG. 2a afterflattening into an oval contour.

FIG. 2c shows a side view of the connecting element shown in FIG. 2a.

FIG. 2d shows a side view of the connecting element shown in FIG. 2bafter flattening.

FIG. 2e shows a second plan view of a connecting element after insertioninto a contact housing.

FIG. 2f shows a plan view of the connecting element shown in FIG. 2eafter flattening into a trapezoidal contour.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows, in an exemplary embodiment, a contact element 1 that canbe used, in particular, for making electrical contact to a sensingelement of a gas sensor with electrical supply leads. Contact element 1essentially comprises a contact housing 62 with a preferably cylindricalouter contour, at least one connecting element 35 located therein, and asealingly enclosing metal sleeve 90. On two end faces 66, 67 of contacthousing 62, electrical lines 2, 20, 22 lead out of contact element 1 toa sensing element (not depicted here) and to an analysis unit (also notdepicted here). Arranged inside contact housing 62 is at least oneconnecting element 35 that provides a stable electrical connection tolines 2, 20, 22.

A description is given below of an embodiment with two incoming and twooutgoing electrical conductors that are connected inside contact element1. Embodiments with only one or with more than two conductors are,however, also possible. With only one line, for example, a ground can beled in via metal housing parts. The electrical line arriving from thesensing element (not depicted here) of the gas sensor must be bothvibration-resistant and temperature-resistant, since gas sensors of thiskind are preferably used at measurement locations at which temperaturesof more than 800° C. can exist, for example in the vicinity of acatalytic converter in an exhaust system of a motor vehicle. In theembodiment depicted, the stiff flexural electrical line 2 comprises twoindividual connecting conductors 8 and 10, insulated from one another,that can be embodied, for example, as wires or as braided or twistedstrands of silver, copper, or other materials suitable as conductors.These connecting conductors 8 and 10 are enclosed by a metal-sheathedline 4 and are separated from one another by insulation. This insulationcan be, for example, a ceramic powder insulator 6 or atemperature-resistant insulator of some other kind. A ceramic powderinsulator 6 of this kind has, in addition to the desired insulatingeffect, the favorable property of damping vibrations and thus toreducing the risk of breakage of line 2 due to shock, sudden impact, orvibrations. In order further to reduce such risks, the free length ofline 2 as a connection between the sensing element and contact element 1is made as short as possible, the minimum length is defined by themaximum temperature resistance of contact element 1 and of the sealingelements made of elastomeric material located therein.

Metal-sheathed line 4, with connecting conductors 8 and 10 that lead outtherefrom and are preferably configured as round, oval, or flat contactlugs 12 and 14, opens into a matching opening 80 in contact housing 62.This opening 80 is located centrally in one end face 67 of contacthousing 62, and has a chamfer 84 for better and easier insertion ofmetal-sheathed line 4. This chamfer 84 can, for example, have a bevel of15 degrees or more. The depth of chamfer 84 is advantageously selectedso that it represents more than 5% of the diameter of opening 80 inorder to constitute an effective insertion aid. At a specific distancefrom end surface 67 that, for example, can correspond to the diameter ofopening 80, opening 80 has a constriction 82 that acts as a stop formetal-sheathed line 4. This constriction 82 acts at the same time as aguide for contact lugs 12 and 14 which preferably are bent slightlyoutward prior to insertion, so that as metal-sheathed line 4 is insertedthey can be pushed into a defined position in contact housing 62. Alsoprovided, for exact guidance of these contact lugs 12 and 14 into theirfinal position, is a central wedge 64 with which contact lugs 12 and 14are deflected apart as metal-sheathed line 4 is inserted.

Provided for each of the at least one connecting lines 20, 22, at an endface 66 of contact housing 62 located opposite end surface 67, is around or rectangular receptacle 68, 70 in each of which a connectingelement 35 is installed with an interference fit and in a form lockingmanner. Connecting element 35, which is made, for example, of metal,overlaps one of contact lugs 12, 14 with a preferably flat end 36, 38,and has at the other end a receptacle for a connecting line 20, 22 whichcan retain the latter by clamping or crimping and at the same time cancreate an electrical contact. Electrical connecting lines 20, 22comprise a core 24, 26, made for example of copper wire or silver wire,and a respective insulating casing 28, 30. Contact elements 35, whichresemble a cable lug, possess an elongated contour and each have twoopen rings 40, 42 and 44, 46 that can each be squeezed together in orderto embrace a stripped end 32, 34 of electrical lines 20, 22. Rings 40,42 in a central region of contact element 35 have a diameter suitablefor receiving a core 24, 26 of lines 20, 22. The separately squeezablerings 44, 46 have a diameter suitable for receiving core 24, 26 togetherwith insulating casing 28, 30 of lines 20, 22.

Resting flush against the flat end face 66 of contact housing 62 is acylindrical sealing element whose outside diameter correspondsapproximately to that of contact housing 62 or is slightly larger. Thissealing element is preferably embodied as elastomer nipple 52, and hasfor each of the at least one connecting lines 20, 22 a leadthrough 54,56 that corresponds exactly to the outside diameter of connecting lines20, 22.

Contact lugs 12, 14 of connecting conductors 8, 10 are connected to thecorresponding contacts 36, 38 of connecting elements 35, preferably bylaser welding. These weld points are labeled here as connecting points48, 50. To make these connecting points 48, 50 accessible from outside,contact housing 62 has corresponding radial apertures 72, 74 that can beof circular or oval configuration.

A protective sleeve 90 that preferably is made of metal is provided inorder to seal off contact housing 62, with the electrical connections,from the outside in sealing and heat-resistant fashion. The contour ofthis protective sleeve 90 corresponds to the outer contour of contacthousing 62, so that after laser welding of connecting points 48, 50, itcan be slid axially over contact housing 62 in the direction of end face67. Protective sleeve 90 is constricted at an end facing toward end face67, specifically the side facing toward connecting line 2 andmetal-sheathed line 4, so that at this point its inside diameterapproximately equals the outside diameter of metal-sheathed line 4. Assoon as protective sleeve 90 has been slid over contact housing 62 andcomes to a stop, it can be sealingly joined to metal-sheathed line 4 bylaser welding. This continuous annular weld is illustrated by contactpoint 92. Protective sleeve 90 is of correspondingly longerconfiguration than contact housing 62, so that it additionally fitsaround elastomer nipple 52 over its entire length. By compressing oredging over protective sleeve 90 to a smaller diameter 94 over theentire length of elastomer nipple 52, the latter is compressed andcompletely seals the interior of contact housing 62 from the outside.Elastomer nipple 52 is preferably made from a heat-resistant material,for example silicone, Viton, Kalrez, or the like. Insulators 28, 30 oflines 20, 22 are also preferably made of temperature-resistant material,since lines 20, 22 are located in a thermally affected zone in whichvery high temperatures can occur.

FIGS. 2a through 2 f show several side views (2 c, 2 d) and plan views(2 a, 2 b, 2 e, 2 f) of a connecting element 35 that is immobilized incontact housing 62 and that, for example after insertion into contacthousing 62, can be pinched in such a way that it is impossible to pullout. After insertion, it is possible to create from a circular contourof one of rings 40, 42, 44, 46, or also of an additional ring 37 (FIG.2a) that is not used to clamp a line 20, 22 or a core 32, 34, forexample an oval (FIG. 2b) or a trapezoidal contour (FIG. 2f). Connectingelement 35 is thus immobilized in its position and can no longer bepulled out.

FIG. 2a shows connecting element 35 after insertion, in plan view. FIG.2b shows a connecting element 35 with an ovally pressed contour that isthus protected from being pulled out of contact housing 62. FIGS. 2c and2 d show corresponding side views. This compression can preferably beaccomplished through radial housing openings 72, 74, through whichjoining by way of laser welding is subsequently also accomplished. FIGS.2e and 2 f show an alternative contour after insertion (FIG. 2e) andafter pinching (FIG. 2f), with a trapezoidal contour.

What is claimed is:
 1. A contact element for making electrical contactto a sensing element of a gas sensor, comprising: at least oneconnecting conductor guided in a metal-sheathed line; at least oneflexible connecting line contacting the at least one connectingconductor at a connecting point; and a contact housing allowing sealedand temperature-resistant contact between the at least one connectingconductor and the at least one connecting line, the connecting pointbeing situated in the contact housing, the contact housing including: atleast one connecting element situated in the contact housing in aform-locking manner and with an interference fit, the at least oneconnecting element contacting the at least one connecting conductor andbeing immovably joined to the at least one connecting line, and atemperature-resistant protective sleeve enclosing the contact housing,the protective sleeve being joined directly to the metal-sheathed lineand the at least one connecting line.
 2. The contact element accordingto claim 1, wherein the contact housing is made of atemperature-resistant, electrically insulating, and mechanically stiffmaterial.
 3. The contact element according to claim 2, wherein thetemperature-resistant, electrically insulating, and mechanically stiffmaterial includes ceramic materials.
 4. The contact element according toclaim 2, wherein the temperature-resistant, electrically insulating, andmechanically stiff material includes thermosetting plastic.
 5. Thecontact element according to claim 1, wherein the contact housingfurther includes a recess for each of the at least one connectingelement, the recess being located in a longitudinally extendingdirection of the contact housing.
 6. The contact element according toclaim 5, wherein the contact housing has a substantially cylindricalouter contour.
 7. The contact element according to claim 1, wherein theprotective sleeve is made of a weldable metal.
 8. The contact elementaccording to claim 7, wherein the protective sleeve surrounds thecontact housing in a flush manner.
 9. The contact element according toclaim 8, wherein the protective sleeve has an outer contour that tapersat a side facing toward the metal-sheathed line, the outer contourtapering so that the protective sleeve fits flush around themetal-sheathed line.
 10. The contact element according to claim 9,wherein the protective sleeve is sealingly joined to the metal-sheathedline.
 11. The contact element according to claim 10, wherein theprotective sleeve is joined to the metal-sheathed line via a continuouslaser weld.
 12. The contact element according to claim 1, wherein thecontact housing further includes a substantially cylindrical elastomernipple, the elastomer nipple being arranged coaxially with the contacthousing and terminating flush with a first end face of the contacthousing.
 13. The contact element according to claim 12, wherein theelastomer nipple has a leadthrough for each of the at least oneconnecting line, the lead through enclosing the at least one connectingline in a flush manner.
 14. The contact element according to claim 13,wherein the protective sleeve encloses the elastomer nipple, theelastomer nipple resting flush against the first end face of the contacthousing.
 15. The contact element according to claim 14, wherein theelastomer nipple is made of a heat resistant material.
 16. The contactelement according to claim 15, wherein the heat resistant materialincludes at least one of silicone, Viton, and Kalrez.
 17. The contactelement according to claim 13, wherein the elastomer nipple is crimpedby the protective sleeve, the protective sleeve enclosing andcompressing the elastomer nipple.
 18. The contact element according toclaim 12, wherein the contact housing further includes a central openingon a second end face opposite the first end face, the central openinghaving a diameter corresponding to a second diameter of themetal-sheathed line.
 19. The contact element according to claim 18,wherein the central opening includes a chamfer.
 20. The contact elementaccording to claim 19, wherein the central opening has a conicalconstruction, the conical construction being axially spaced away fromthe chamfer.
 21. The contact element according to claim 1, wherein theat least one connecting conductor includes a contact lug.
 22. Thecontact element according to claim 21, wherein the at least oneconnecting element has a flat end overlapping the contact lug, thecontact lug being laser welded to the flat end.
 23. The contact elementaccording to claim 22, wherein the contact housing has a radial aperturesituated at each connecting point for the contact lug and the flat end.